The present invention relates to a hydraulic cylinder structure in general and more particularly to a structure having a seal-less piston.
Hydraulic cylinders, such as master cylinders and slave cylinders of hydraulic control systems for operating the clutch, the transmission or the brakes of a motor vehicle, for example, are conventionally made of a housing cast of metal or of a plastic material provided with a cylindrical bore in which is disposed a reciprocable piston. The piston is conventionally provided with at least one groove in which is placed an annular seal of elastomeric material which prevents leakage of hydraulic fluid from the high pressure side of the piston to the low pressure side. When the structure of the hydraulic cylinder is that of a master cylinder, an input member in the form of a rod is attached to the free end of the piston for reciprocal displacement of the piston within the cylinder and for causing flow of hydraulic fluid from and into the pressure side of the cylinder on the other end of the piston. In structures adapted to operate as a slave cylinder, hydraulic fluid is introduced via an appropriate conduit from the outlet of the master cylinder to an inlet into the slave cylinder on one end of the piston and an output member is attached to the other end of the piston for operating a component such as the gear shift rail of a transmission, the throw-out bearing of a mechanical clutch, or the wheel brake mechanism of a motor vehicle, for example.
In structures wherein the cylinder housing is made of plastic, a metallic tubular liner is affixed in some manner within the bore of the housing to limit wear of the bore wall caused by the reciprocating piston and piston seal.